Chemical pollution threatens Europe’s freshwaters

Chemical pollution threatens the health of almost half of all European freshwaters, according to a new study in Proceedings of the National Academy of Sciences (PNAS). Researchers from German, French and Swiss universities used data from 4,000 monitoring sites across Europe to calculate the first continental scale ‘risk assessment’ of the impact of toxic organic chemicals on freshwater ecosystems.

Their study, “Organic chemicals jeopardize the health of freshwater ecosystems on the continental scale” suggests that chemical pollution has acute, potentially lethal, impacts on freshwater organisms at more than one in ten sites across Europe (Map A); and long-term negative impacts at almost half of monitored sites (Map B). The maps suggest that the impact of chemicals is less severe in Southern Europe, although the authors suggest that this may be due to monitoring limitations in these areas.

Pesticides from farming were responsible for the majority of acute chemical risks to freshwater life in the study. The impact of chemical pollution on freshwaters was significantly increased close to agricultural land, sewage treatment works and urban areas where there is run-off of pollutants into rivers.

In this study, which supports the EU SOLUTIONS project, monitoring data from the European Environmental Agency’s Waterbase database was used to plot the mean and maximum annual concentrations of 223 organic chemical compounds at 4,000 sites on 91 river basins across Europe. At each site, ‘risk thresholds’ of pollutant levels were calculated for three biological indicator species: the fathead minnow (Pimephales promelas); daphina, or water flea (Daphnia magna), and algae (Pseudokirchneriella subcapitata). These three species were selected because there is a wealth of existing laboratory data on their responses to pollution, and as they are a range of taxonomic groups (fish, invertebrate, algae) at different tropic levels in the food chain, they potentially give a good indication of overall ecosystem health.

Risk thresholds indicate the point at which concentrations of chemical pollutants threaten the health of these aquatic organisms. The research team calculated two risk thresholds for pollutant levels: an acute risk threshold, defined as one-tenth of immediately lethal concentration; and a chronic risk threshold at one-thousandth of lethal concentration. The team state that biodiversity losses have been observed in this second chronic category, despite the high level of dilution. These calculations of thresholds for chemical pollution concentration were then combined to produce a chemical risk calculation for each river basin, shown in the maps above.

Pesticides from agricultural run-off posed the most acute chemical risk to freshwater life in this study. However, other chemicals were found to occur at potentially damaging concentrations, including the banned biocide tributyltin (an antifouling agent that is leached from ship’s hulls), brominated diphenyl ethers (which is used as a flame retardant in consumer goods) and polycyclic aromatic hydrocarbons (which are released from fossil fuels).

It is suggested that EU laws which control the use of ‘priority’ chemicals deemed particularly hazardous to the aquatic environment may not go far enough in protecting freshwaters from chemical pollution. Co-author Werner Brack from the Helmholtz Centre for Environmental Research in Leipzig, Germany explains, “Fortunately the use of many of these priority substances is no longer permitted and therefore, their concentration levels are steadily decreasing in many parts of the European streams. The real problem, however, is that a large number of chemicals which are currently in use are not taken into account at all in the context of water quality monitoring.”

It has long been known that chemical pollution has potentially lethal impacts on freshwater ecosystems, especially given that is just one of multiple stressors affecting the aquatic environment. However this new research suggests that the negative effects of chemical pollution are more widespread across Europe than previously thought.

Ralf B. Schäfer, head of the research team from the Institute for Environmental Sciences in Landau, Germany suggests, “Generally speaking we probably underestimated rather than overestimated the risks in our analyses. The actual state and condition of European freshwater ecosystems is probably even worse.” This in turn casts doubt on whether the ecological targets for European freshwaters set by the Water Framework Directive for 2015 will be met, and for the long-term health of the ecosystems if chemical pollution isn’t better managed in the future.

To address this, the authors suggest that large-scale, integrated pollution management approaches that go beyond local-scale ‘end-of-pipe’ solutions are critically needed. There are two key stages for management here: prevention and monitoring. The prevention stage involves promoting ‘green’ chemistry and the substitution of toxic chemicals in industry, agriculture and manufacturing processes, alongside effective treatment and disposal of chemical waste. It is suggested that pesticide reduction in agriculture and the use of riparian buffers at the edges of farmland are needed to reduce the amount of chemical pollution downstream of agricultural land.

The authors argue that the monitoring stage of management should better account for the ∼100,000 organic chemicals in daily use which may enter freshwater ecosystems via numerous different routes. Instead of focusing on individual chemical pollutants, it is suggested that management which monitors (and ideally mitigates) toxic pressure as a whole is necessary. Similarly, the study emphasises that chemical pollution is a large-scale process, and needs to be addressed as such through frameworks such as the Water Framework Directive and Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH).

Putting such large-scale initiatives which require a shift in the way that the public, industry and agriculture use and dispose of chemicals is likely to prove a major challenge. However, the bleak picture that this study paints may well prove an important catalyst for future political and public action.

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